The effects of hypertension on the compostition of the cytoplasm and cell organelles of vascular smooth muscle and of the paracellular matrix will be determined by electron probe analysis of cryo sections of rapidly frozen blood vessels. In order to ascertain which of the changes in hypertension are due to the effect of increased wall stress on vascular smooth muscle and which are causative in the mechanism of hypertension, these initial studies will be conducted on preparations in which hypertrophy and hyperplasia of vascular smooth muscle have been induced by increased mechanical stress. Specific questions to be answered are whether, in hypertensive vascular smooth muscle, hypertrophied rough endoplasmic reticulum is a calcium storage site and whether the mitochondrial Ca content is increased. We shall also compare the affinity of the in situ smooth endoplasmic reticulum (SR) and mitochondria for Ca in hypertensive to that of normal vacular smooth muscle, and measure the alterations in cellular monovalent ions induced by increased wall stress.